While MS and Sony have marketing deals, I don't think they include deals to intentionally hold back on the game performance and graphics. I could be wrong, and if I am, it would be Sony that is doing it. Phil from Microsoft has stated that they do not ask that their partners dumb down their games on the competing consoles. He said that isn't fair for the gamers.
I think if that were true, then Star Wars on the PS Pro would look the best...but we have heard from two people at MS now that Star Wars will look best on X1X.
Again, I could be wrong, but there is no benefit to the gamer nor the developer. Developers want to sell their games and have them seen in the best possible light.
That is my opinion.
Well I didn't say dumb down on purpose, but deals can, & will get you added improvements/content.
Phil has said things in the past against paying for 3rd party exclusives, yet they still pay to get them... He's not entirely reliable